The present invention relates to a manufacturing method for waveguide-type optical components, and more particularly, to a method for manufacturing waveguide-type optical components with a lower propagation loss at a low cost.
To fabricate optical fiber communication systems for an extensive field of applications, it is necessary to supply, in a high volume at a low cost, optical components such as optical couplers/splitters and optical multiplexers/demultiplexers to be incorporated in the systems. There is especially high demand for high-volume and low-cost supply of the waveguide-type optical components, which use silica glass as the main material, because they ensure good coupling with optical fibers and provide excellent optical propagation. The electron beam irradiation is attracting attention in the industry as a method for manufacturing waveguide-type optical components, which is capable of responding to the demand described above and which requires a relatively low man-hour and a lower cost. Concerning the optical component manufacturing method based on the electron beam irradiation, for instance, a thesis titled "Optical channel waveguide fabrication based on electron beam irradiation of silica" by S. J. Madden et al. appeared in Applied Physics Letters, Vol. 57, No. 27 issued on Dec. 31, 1990, and another thesis titled "Waveguide Fabrication for Integrated Optics by Electron Beam Irradiation of Silica" by D. Barbier et al. appeared in Journal of Lightwave Technology, vol. 9, No. 6 issued in June 1991.
According to the conventional typical electron beam irradiation method, an antistatic layer composed of aluminum, for example, and a thin-film layer composed of gold, for example, are formed in turn on a lower clad section which is formed on a Si substrate and which is made of silica glass. Then, only a portion of the thin-film layer, which corresponds to a waveguide pattern, is removed from the thin-film layer to form a mask layer of the desired pattern, and an electron beam is irradiated from above the mask layer. In that portion of the lower clad section which is subjected to the electron beam irradiation, the silica glass contracts and produces a higher refractive index than the other portions, thereby forming a core. Lastly, the mask layer and the antistatic layer are removed in turn. In this manner, waveguide-type optical components, in which cores with the desired patterns in the lower clad assemblies exist as the waveguide routes, can be obtained at a relatively low cost.
However, as is generally known about the film forming technology, the surface of the lower clad section does not become completely smooth and flat, but develops minute irregularities. As a result, in an optical component manufactured in such a manner, the top surface of a core formed in the lower clad section is in contact with the foregoing minute irregularities of the lower clad section, and then the top surface of the core is exposed to the atmosphere. Under such a condition, the light, which goes through the core, increases its scattering loss due to the foregoing minute irregularities. Consequently, the propagation loss, which is partly caused by the scattering loss, increases.